#12538: XO-4 CPU usage at idle is high
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Reporter: dsd | Owner: cjb
Type: defect | Status: new
Priority: normal | Milestone: 4-software
Component: not assigned | Version: not specified
Resolution: | Keywords:
Next_action: never set | Verified: 0
Deployment_affected: | Blockedby:
Blocking: |
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Comment(by dsd):
I tested some different vanilla kernel versions, comparing against our
OLPC kernel. Booting without X, running "top" and watching the idle % for
about a minute.
{{{
olpc 3.5: 85%, varying +/- 5%
olpc 3.5 nohz=off: 96% constant
3.5: 99%, frequently fluctuating all the way down to 0% for no apparent
reason
3.5 nohz=off: 99% constant
3.5.7 behaves the same as 3.5
3.6: 98%, frequently fluctuating all the way down to 0% for no apparent
reason
3.6 nohz=off: 99% constant
3.7: 96% , varying +/- 3%
3.7 nohz=off: 98% constant
}}}
Conclusions:
* All the kernels behave badly with nohz enabled, up until 3.7. Will
explore the possibility of disabling nohz for now on XO-4 - main
consideration is impact on power usage.
* Something in the OLPC 3.5 kernel causes behaviour to differ from the
vanilla 3.5 kernel. Or it could be a difference in .config. It would be
nice to know what this is.
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Ticket URL: <http://dev.laptop.org/ticket/12538#comment:5>
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